harry potter - How does the wizarding community handle covers ups?

Places of significant importance in the wizarding community (whether because of magical properly or deemed significant by society) are hidden from Muggles. For example: disguising Hogwarts as a ruined castle, Diagon Alley only being accessible by Floo power, Apparation or the hidden entrance to the Leaky Cauldron.

We see that the Ministry takes action against underage magicians practicing magic outside school, such as when Harry blows up his aunt or uses a Patronus. But later in the series, we see wand firefights on broomsticks taking place on busy streets, in full view of Muggles.

How does the wizarding community handling the cover ups of public magical incidents in the Muggle community (from small ones like Harry's aunt blowing up to large scale wand firefights) which could be reported on the news?

Also, in the off chance that the Harry Potter series also took place during the advent of the smart/camera phone, is there any reference to how phones may have affected these cover ups or how the process was adapted to deal with advancing muggle technology?

Answer

The Ministry have dedicated staff for handling cover-ups.

We see at least three different types of response in the canon:

1. 
   

   Memory modification.

   
   

   When Harry blows up his aunt, Cornelius Fudge later explains that her memory was modified (probably using something like Obliviate) to keep her from remembering anything:

   
   

   
   

   “Now then… You will be pleased to hear that we have dealt with the unfortunate blowing-up of Miss Marjorie Dursley. Two members of the Accidental Magic Reversal Department were dispatched to Privet Drive a few hours ago. Miss Dursley has been punctured and her memory has been modified. She has no recollection of the incident at all. So that's that, and no harm done.”

   
   

   — Prisoner of Azkaban, chapter 3 (The Knight Bus)

   
   

   
   
   

   I don’t think we’re told (in the books) about any Muggles who saw her, so we don’t know what happened there.

   
   

   We hear the names of some of the other departments when Harry visits the Ministry:

   
   

   
   

   “Level Three, Department of Magical Accidents and Catastrophes, including the Accidental Magic Reversal Squad, Obliviator Headquarters and Muggle-Worthy Excuse Committee.”

   
   

   — Order of the Phoenix, chapter 7 (The Ministry of Magic)

   
   

   
   

   This seems to be the default, and preferred, option. This department also stepped in to modify the memories of the Roberts family at the Quidditch World Cup

   
   


2. 
   

   Let the witnesses in on the secret, and swear them to secrecy.

   
   
   

   In the case of Harry’s Patronus, the only witnesses were Dudley and Mrs. Figg, both of whom are already aware of the magical community and thus don’t need “dealing with”. Sometimes the Ministry decides to let people be aware of the magical community and tells them to keep schtum; see Why Doesn't the Ministry Ever Modify the Dursleys' Memories? for one example.

   
   


3. 
   

   Some incidents are too big.

   
   

   When Harry and Ron fly the car to London, Snape explains how many Muggles saw them:

   
   

   
   

   “Two Muggles in London, convinced they saw an old car flying over the Post Office tower… at noon in Norfolk, Mrs. Hetty Bayliss, while hanging out her washing… Mr. Angus Fleet, of Peebles, reported to police… Six or seven Muggles in all. I believe your father works in the Misuse of Muggle Artifacts Office?” he said, looking up at Ron and smiling still more nastily.

   
   

   — Chamber of Secrets, chapter 5 (The Whomping Willow)

   
   

   
   

   Although the books predate smartphones (more on that in a sec), this is probably too big to cover up completely without causing more suspicion. (Consider the Streisand effect.) It would likely be reported in local newspapers or in police reports, which can’t be easily mass-modified. If the individuals who originally saw the car suddenly had no recollection of the incident, then the story would gain a lot more traction. As it is, the whole thing will probably be forgotten within a week or so, because people.

   
   
   

   We see the Ministry struggling again in the midst of the second war with Voldemort. Here they’re trying to cover up a giant rampage, and it’s clear that their systems aren’t really up to large-scale cover ups:

   
   

   
   

   “The Office of Misinformation has been working around the clock, we've had teams of Obliviators out trying to modify the memories of all the Muggles who saw what really happened, we've got most of the Department for the Regulation and Control of Magical Creatures running around Somerset, but we can't find the giant – it's been a disaster.”

   
   

   — Half-Blood Prince, chapter 1 (The Other Minister)

   
   

   
   

Most incidents are probably fairly small with a handful of witnesses, and can be handled with memory modification (case 1). There are special cases like the Dursleys (case 2). The large-scale cases which can’t be covered up completely (case 3) seem comparatively rare.

The books take place between 1991–8 (based on Nearly Headless Nick’s Deathday party in Chamber of Secrets), which predates the first cameraphone by about a year or so (according to Wikipedia). But digital cameras existed, as did regular film cameras.

I don’t believe it’s ever been explained how the Ministry would deal with cameras, or networks like Twitter and Instagram where images of magic can go viral.